where \(\mu =\frac{\sum n_{j}}{4\pi \textit {V}}\) . Using the spectral decomposition theorem, the respective Cauchy stresses of the incompressible network can be derived from the strain energy density function \(W(\lambda )\)  as [1]}
\({\sigma }= \sum _{k=1}^{3} \lambda _{k} \frac{\partial W}{\partial \lambda _{k}} ({n}^{(k)}\otimes {n}^{(k)})\) 
